Ok, you've convinced me to try some agastache plants, but in addition I would like to sow some A. foeniculum seeds to compare. Advice on when to sow those on the web is scarce and somewhat conflicting:
Indoors 6 to 8 wks before first frost (2 references)
Indoors 8 wk before first frost (1 ref)
Outdoors after last frost (1 ref)
Indoors Mid Feb to Mid March (1 ref)
Wintersow (2 ref) (I have had mixed results wintersowing with other flowers.)

Which sowing method/time would you recommend for these seeds in CT (Zone 6a) ?

This is a very easy species to grow from seed. I would use whatever method fits your facilities the best. They are pretty undemanding. If you start 6 to 8 weeks before you can set them out, you will have some pretty substantial plants ready to go.

If at all possible, start with fresh seed. I was disappointed several years in a row when trying seeds of unknown age. Once a friend sent me some fresh seeds, it was as easy as can be. I used the winter sowing method in 2011; sown Feb. 15, and sprouts by March 5. I ended up with 72 transplants!

If you're not sure about the freshness of your seeds, you might try test germinating a few by using the baggie method (indoors) first.

Best of luck to you! Once you do get a few plants going they'll reseed just enough that you'll likely never be out of them.